Just how does the water in a closed loop system become "permanently polluted"?
What happens to the water when the data center is no longer useful? In theory it is cleaned up before it goes under, but we all know that always happens as designed. What about leaks? Mistakes by the maintenance crew, sabotage, plain old screw ups, or weather induced damage? Even the air exchange in the cooling towers, do any chemicals fly off in the evaporation cycle? How many PPM, PPB are truly safe? What's "safe" today maybe determined to be a toxic level in only a few years.
From my dealings with the attempted solar project. Cleanup is listed in the papers, BUT it isn't complete clean up. Soil requirements are only down to three feet, or something similarly small, (rusty memory) beyond that depth the landowner is on the hook. The same time they limit clean up depth they let you know they will be working about double that depth.
Again, as said above, use brown fields for all of it. Brown fields, parking lot roofs, manufacturing roofs etc. Data centers, since they can be anywhere, put them in non tillable areas. Wind, has it really been proven to be a net positive? (including clean up costs) I have climate issues with wind no one can answer.
Before I get a greenie attack. Solar farms on the west coast. It has been shown Pacific winds make it roughly to central U.S. and affects the ecosystems. (this is going to be kind of vague as I learned this many years ago) these areas rely on certain amounts of wind. Let's say that an area has received 4mph winds for eons and the local plants have adapted to that constant. Now with wind farms spinning away in CA the wind that makes it through is now only 2.5 or 3 MPH, or even less, what happens to the native flora and fauna over this change? Nothing? Plants species die? Animals that fed off of these species of plants? We don't know, and these type of studies are so rare we may never know until it's too late.
BTW- I apply this question to the wave generators of the coast too.
I am by no means treehugger, but that doesn't mean we shouldn't REALLY look at this from a future perspective.